MG MGB and MGB GT Tech Talk
I'm getting ready to rebuild my Weber carb on my 79 B. It's a 32/36 DGV 5A. I haven't performed a rebuild in many years. I have the block diagram of the carb but no instructions. Is there anything to watch out for during the disassembly/assembly? Thanks for your help.
Wayne
Well, first get a good, complete rebuild kit BEFORE you disassemble. Don't try to piecemeal it. Get yourself a fairly large, fairly clean, flat surface (3'x3'). Buy some carb cleaner or whatever, have rags and paper towels nearby. Take it off the car before you disassemble! Take some digital photos along the way to enhance memory. :S Don't be in a hurry. Have fun!
Taking it off the car may or may not be tricky depending on how you have the choke and throttle linkage (and return spring) attached. When you pull apart the major sections you will be disconnecting the butterfly arm the choke linkage is attached to. There is a tiny, tiny, tiny cotter pin holding that on to the butterfly - easier to take off than to put back on (for me, anyway). Be careful with the floats not to bend anything.
The guide inside a good rebuild kit will tell you the rest, I think.
Dave
Thanks David. Unfortunately, the Moss kit only contains a block diagram of the carb showing each component. I think that may be sufficient. There's no instructions. There's a few of the rubber o rings and copper washers that I'm trying to find the propper home for. I think if I go slowly, I'll figure it out from the block diagram.
OK, I'm baffled. On the below diagram, you will see diagram #s 38, 38A, 39, and 40. These are respectively the primary idle jet, secondary idle jet, the gaskets (2 ea.) for idleing jet holder, and idling jet holder (2 ea.). The diagram makes it look like #s 38, 39, and 40 are located beneath the accelerator pump diaphragm assembly (#36). There are two indentations below the diaphragm assembly but NO slotted head of the idling jet holder (#40). I probed around in the circular indention and even dug out some of the pot metal and found nothing but more pot metal below the surface. The dashed line showing the location of 38, 39 and 40 must be erroneous.
I also can't tell from the diagram where the 38A, 39 and 40 (secondary idle jet) enters the carb. There's no dashed line showing the location of the three parts. Has anyone come across this issue before. I bet it's something obvious.
Wayne
Sorry, I forgot to paste the link mentioned in the above message. Here it is for reference:
http://81.191.169.162/pub/weber_carburetor_schematics/32_36DGV.pdf
in the attached image you will see the indentation mentioned above. The carb diagram indicates the idling jet holder is in the indentation shown at the point of my pocket knife blade. There's nothing there.
It goes into the space on the left side of the pump cavity, which is on an angle. RAY
This is what your looking for. 38A is the same location on the opposite side of the carb. Make note of what size jet you pull from each location. The idle jets, mains, airs, and emulsion tubes are all different sizes so they will need to go back in the same locations. Also check your float height after reassembling everything. There are also jet sizes in the library so you can see if you are jetted correctly. http://www.mgexperience.net/article/3236dgev.html
I have had good with the jetting listed in the library. (using the .60 on the primary idle)
Ray and Bryan:
Thanks for helping. I finally figured it out. The diagram that came with the kit was possibly copied too many times making the dashed line look like it was going to the wrong place. Common sense finally prevailed. I ended up with two left over parts. One very small(~3 mm dia.)rubber o ring and a ~1.5 in. round paper gasket. I could not find either on the kit diagram or carb. Hopefully they are not show stoppers.
Bryan: What is the float measurment supposed to be? How do you measure it. What surface are you measuring from/to?
Wayne
Here is a link showing float heights. Yours will either have plastic or brass floats, use the chart for which one you have.
http://www.piercemanifolds.com/v/vspfiles/templates/34/images/float_1.jpg
To set the height hold the cover vertically with the gasket in place. Measure from the bottom of the base with gasket, to the bottom of the float with the float just resting on the spring loaded ball. After setting that adjustment lay it over flat and let the float drop down and again measure from the bottom of the gasket to the bottom of the float.
I have made my own tools for measuring. See diagram below. Measurement is from the outer edge (this is where it rest on the carb cover) to the inner edge. (this is where the bottom of the float touches when at 41mm or whatever your setting is) The tool is only as accurate as you make it and you will need one for both settings.
Did not mean to abandon you, Wayne, but had military duty all weekend with no access in the secure area. You got the help you needed. I would add that Pierce probably has an exploded view of the carb on its site that may be helpful. I'll also add that buying a whole new one from Pierce is pretty darn reasonable!
Dave
Bryan: Thanks for the float setting procedure. I checked it out today. The float was right where it was supposed to be.
David: Thanks for checking back in.
I installed the carb and got the engine to start. That's great news. It idled fairly smoothly with the manual choke all the way closed. I let the engine warm up and gradually started opening the choke. The engine kept wanting to die as the choke was opened even at operating temp. I took it for a 2 mile drive. The whole time the engine wanted to surge. It would run smoothly for about three to four seconds and then try to stall, then try to take off for another 3 to 4 sec. That pattern went on and on until I returned. The engine did better with the choke more toward the closed position but would surge or cycle at all choke positions. Any ideas what is happening? How to remedy?
Wayne
Vacuum hose re-attached to the dizzy? If yes, I would suspect you've re-installed something slightly out of place or a tiny bit of crud has been loosened and crept into a passageway it shouldn't be in. :(
Dave
The vacuum hose is connected. I hope it's not crud. I found a carb tuning procedure for this carb. I'll try that and see if it helps. I probably would have been better off buying a new weber carb. It would have been tough to improperly install one of the parts. Swap out was pretty straight forward.
This car sat under a carport in Houston, TX for several years. It had become a home for "Mud Dobber's". I bet I've cleaned a five gallon bucket of Dobber nests out and off the car. I wonder if the Mud Dobber's nested in the exhaust pipes and/or muffler. I saw exhaust smoke coming from the pipe yesterday. I guess a partial obstruction could theoretically cause the surge problem.
It's more likely the carb that's the issue. Time to do some more tinkering.
Wayne
Here's a link to the best written tuning guide I know of. http://www.justbrits.com/Articles/TuneWeber.html
If you haven't checked the timing I would do that also. DGV's seem to be happy somewhere close to 15 btdc.
Bryan: Good to get your endorsement on this one. I found the same one last night. It seems like a good one. I appreciate your help!
Wayne
I worked on a BMW motorcycle, a few years back. When I finally started it up, I almost fainted at the racket that it produced. It turned out that mice had been nesting in the exhaust system. It seems that the bike had been garaged next to a large container of dry dog food. Yup. The little devils had carried their stash back to the BMW and when it started up all of the dog food pellets flew out and hit the metal door in the repair shop, making a dreadful noise and scaring the crap out of me. RAY
I did some more tinkering today. I made it through the first 5 steps of the procedure at http://www.justbrits.com/Articles/TuneWeber.html. I couldn't get the engine to idle (after warm up) without a fully closed choke. I then decided to further open the idle mixture screw (base of carb) with an open choke. The engine started smoothly idling when the idle mixture screw was at about 3.5 turns from the bottom. According to the procedure anything outside the range (0.5 - 2.5 turns form bottoming) might be an indication of improper rebuild/jetting.
Even after I got the engine to smootly idle (3.5 turns) any movement of the throttle would induce an engine stall. Where would you go from here? What other things could be at issue (timing, carb plumbing, trashed carb, bad rebuild, jetting, etc.)
On a postive not this engine is now running after about 8 to 10 years of silence. That's a big positive. Today, it immediately started with only a slight bump from the starter.
Thanks for the story Ray.
Wayne
It really helps immeasurably to have the book to refer to, especially in your case. Many of these carburetors are shipped new with "standard" jetting. Unless part of a package, that was specifically designed for the 1800 B engine, it's more than likely that you have incorrect jets installed for your application. RAY
Ray:
Where do I find the book you are refering to? Is suppose improper jetting is likely. Ther must be a way to measure the jets and match them to my engine. I have no idea what the previous owner did to the carb. I bought it in a "not running" condition.
Wayne
Ray:
It seems Bryan already supplied me with the link to the library material on the Weber carb (above). The article gives jet sizes.
General DGV settings for a unmodified MGB
• Idle jets of .55 or .60 and secondary of .50 (approx)
• Main jet is 140 and secondary is 135
• Air correction is 170 and 160
I wish I had measured everyting when I had the carb apart. I assume the sizes in the article are in millimeters. There are no units. I'll check with Moss to see if they sell the jets. Of course, I need to first find out the measurement of what's in my carb. If they are the correct size, the there's another issue.This little booger sure is giving me a lesson in auto mechanics.
Wayne
I found the article in the library (previously supplied by Bryan).
The jets have the sizes stamped on them. The numbers are small and you may need a magnifying glass to see them. Some people have posted good results with jets sized other than listed in the library. I have had good luck with the listed jetting in 3 cars. (using the .60 as opposed to the .55 idle) Before tearing it apart check your timing, if you still dont have any luck then it would be worth checking the jets
to see what you have.
edit- If you removed jets when cleaning but did not take note of what size was where, they may have gotten reinstalled in the wrong location. If you have the smaller secondaries installed where the larger main jets should be, that could possibly account for needing to be 3.5 turns out.
I
just completed this exact task... take out all jets, venturis etc.. soak with carbon cleaner and hit all holes withcompressed air.. repeat!
Bryan:
Thanks for the information. I had no idea how to determine the sizes of each jet. I now know. There's littlc chance I mixed them up. I didn't have them out at the same time. I did a slow one part old, one part new swapping. I'm going to do a good timing on the engine before proceeding.
James:
I have a gallon of carburetor cleaner. However, that stuff is highly toxic. I don't like working with it. I use rubber gloves and goggles when using the stuff. You used the word "carbon" cleaner. Did you mean carburetor cleaner or is there a solvent called "carbon" cleaner that works better. Sorry to be so naive. Did your soaking and compressed air work? Did you have a similar problem with rough running and needing the idle jet to be too many turns in the open direction?
Can any of this be attempted with the carb mounted? I bet the answer is "it shouldn't be attempted".
Wayne
This issue is proving a bit tougher than I thought. The engine will start and idle. It will even idle smothly after warm up with the choke fully open. However, if you even breath on the throttle lever, it will stall the engine. This makes it very tough to do an accurate timing check. After warm up, the engine is idling at about 700 rpms according to my rpm/dwell meter. The manual requires 10 degrees from TDC @ 1500 RPMs. I can't set the RPM because of the engine stall problem. At 700 rpm (idle), with a timing light, the ignition is at about 13 degrees from TDC.
Is it worth removing the carb again, remove and replace jets (as required), remount, readjust or should I invest in a new or professionally rebuilt carb? Can you always fix carburetors with kits or can some be too far gone to salvage? Am I missing something obvious?
Wayne
Keep in mind the specs in the book are not written for a weber. You may have to play with the timing to find where it wants to be. My 70 runs it's best and makes great power at 18btdc at 900 rpm.
There have been a lot of post about the timing mark on the harmonic balancer not being at true top dead center also. So what your seeing with the timing gun has room to be off a touch. Sounds like your close. Try advancing it a little more and see if it will cure the problem. If you take it up the road and you have NO spark knock under load all is well. If you hear spark knock under load, retard the timing enough to eliminate the spark knock. If you advance as far as 18 degrees and see no change there is probably an underlying problem. Let us know if this helps any.
Rebuilding a Weber 36/32 advice
Emulsion tube info
More Weber Info
Weber and Timing
From your description I think you have an air leak. Possibly at the base of the carb, possibly a bent throttle or choke shaft or even a gasket that didn't seal. Please tell me you did not use any permatex or form a gasket anywhere in the carb.
It is also possible that either you or the DPO seated the adjusting screw(s) and the carb body is now junk though the fact that you were able to drive it poses a hope.
Keep in touch I want to know how it turns out.
Bryan:
I'll try to advance the timing a bit and see what happens.
Michael:
I may spray some carb cleaner at the base of the carb, with the engine running, and see if I hear a mometary chage in RPM. That might give me an indication if there's an air leak at that location. The same procedure migh work at other locations too (in theory). I did not use any goop on the kit gaskets. I didn't detect anything on the old gaskets when I removed them. What do you mean when you say "...seated the adjusting screw(s) and the carb body is junk"? I am assuming that closing/tightening the adjusting screws too firmly will cause permanent damage yes/no?
If a leak is found, outside of increasing the torque on the mounting studs, what else can you do to seal the leak?
If no leak is found and the timing is not an issue. It leads back to jetting. If jets are correct sizes they are either clogged or the carb needs replaced. Is that a logical conclusion or is there something else to consider?
Thanks for the help!
Wayne
If you have no leaks, and timing doesnt help any then that will narrow it down some. It sounds like you are making progress. Before tearing it back down, have you gone through the ignition system? Check points gap (unless electronic iginition) check condition of the distributor cap, rotor, wires, and plugs.
If you have gone through the ignition, you have no leaks, have good fuel delivery and timing does not help that most likely brings the fault back to the carb itself. Be it crud inside or incorrect jetting.
Can someone tell me how tight the primary and secondary idle jet(screw/holder) should be? When I installed the O rings on these two jets, I very lightly tightened the two screws (holders). Could this be the source of an air leak, let's say, if they are not tight enough?
I tried squirting carb cleaner around the base of the carb and also at the location of the choke and throttle shafts (other places too). I did not hear any increase in engine RPM. Of course, this assumes that this procedure is even effective.
I also increased the timing up to about 18 deg btdc. The problem was still present no matter what I tried. I'll wait to hear from someone on how tight to tighten the above idle jet screws. Will I damage anything if I firm them up some more? If tightning the screws have no effect, then off comes the carb so I can check the jet sizes.
Wayne
Wayne, I just re-read this from the first post. Somehow I missed your comments on your test drive. That sounds like you are using the fuel in the bowl, then starving, it fills back up, then starves. Wrong float height can cause this. May be worth double checking your measurement. When you have it apart again, that's the time to see what jets you have.
The jets just snug up. You want them tight but it shouldnt require much force. I think Michael was referring to the mixture screw. Running it in tight can damage the needle.
Bryan:
I just replaced the points, condenser, rotor cap and plugs. I didn't replaced the distributor cap or plug wires. The wires look relatively new. Did a spark plug check on #1 and it had a nice spark.I may recheck the points gap and distributor cap condition. There's another guy having a similar Weber DGV carb issue. You may have seen it. I might call Pierce and chatt with them.
Wayne
Bryan:
On page 1 of this thread you gave me a carb float adjusting procedure. You stated:
"To set the height hold the cover vertically with the gasket in place. Measure from the bottom of the base with gasket, to the bottom of the float with the float just resting on the spring loaded ball." Can you define your terminology "just resting on the spring loaded ball"? I have the carb off and I'm rechecking the float. When I hold the cover vertically (ie. rotate 90 degrees from the way it is mounted) how much should the brass tab compress the spring loaded ball? Should it compress it fully or just barely be resting on it. As it is, it fully compresses the ball up into the valve tip at exactly 41mm from the gasket. If the tab is barely supposed to compress the ball, then I would say it's out of adjustment even though it still measures 41mm from the gasket (ie. the ball will compress on the spring 1-2 mm before the ball is flush with the end of the valve tip. Still checking the valve sizes. Will let you know what I find out.
Wayne
When you hold it vertical, it should rest on the ball but but it should not compress the ball in. What kind of tool are you using to measure? You need something similar to the tool I gave a diagram of to be accurate. Pierce sells the tool I shown. I cut mine out of cardboard though. As long as you measure and cut your tool accurate it takes all the guesswork out.
Ok guys:
Here's what I found.
All of my jet sizes are correct with the exception of Primary Air Correction Jet. Instead of having a 170, I have a 165. My Primary Idle Jet is a 0.55 which may not be ideal (0.60) but it's one of the choices in the above list. I think my float needs some tweeking. I made a guage out of a playing card. It is cut as close as I could humanely cut it to 41mm. I made another 51mm guage too. At 41mm the tab is pressing the ball too far up in the valve tip. I will correct that.
THIS is the BIG news. My Secondary Main Jet was completely clogged.I cleaned all of the jets very well. I'm betting the clog in the jet was the problem.
I'll order a new 170 Primary Air Correction Jet. I may as well order a 0.60 Pri. Idle Jet. I hope that finally fixes the carb. Anything else I should check while I've got the carb apart?
Wayne
Yeah, I think ANY junk in the passages will cause you difficulty!
Itty bitty bits of kaka in the passages of these carbs cause FAR more issues than similar kaka in an SU (no small passages).
Cleanliness is absolutely essential.
Doing a rebuild "one bit at a time" will gaurantee that some kaka is missed. The body should be stripped completely, cleaned, passages blown out and then reassembled after the same has been done to the jets, etc.
Be careful of check balls (one-way valves).
When it is in place, manually activating the throttle should give you a nice burst of fuel from the accelerator nozzle.
Good progress! Give us a follow up once it is clean and the new jets are in. Advance auto, Autozone, or your local parts supplier should sell Barryman's Chem-Dip. It comes in a bucket you can soak your parts in.
Wayne, One more thing I didnt see you list. Check the sizes of your emulsion tubes also. They are tubes located underneath the air correction jets. Once the air correction jet is out, flip the carb over and they should drop out. If not they are just held in with crud. Looking for a primary F50 and secondary F6.
I have a bucket of the Chem Dip. I'll check the emulsion tubes to see if they are clear. Let you know if it works this time. Pierce was closed last Friday for inventory. Will order parts Monday.
In the mean time, I'll do some additional cleaning on the carb and weigh into some electrical problems. No horn and most of my warning lights are inop. She's also very leaky in the oil seal department. The engine seems to be in pretty good shape. A little valve noise but that's it. This is what happens when you let a car set for several years.
Wayne
Bryan had a great point about your DGV emulsion tubes. If you are running a F50 and F6 set of tubes your float level will be different than previously discussed. Weber North America advise 35/51mm for plastic floats with F50 emulsion-tubes, or 36.5/46.5 if using an F6 emulsion-tube. Just FYI.. I have done a ton of research on this, so I hope it helps.
Here's an update. Thanks everyone for all of your advice! My emulsion tubes are correct. I have and F50 and F6. Both had some clogged ports. I cleaned them well. I'm now trying to calibrate the float. I have brass floats. Above, Bryan gave me information on the settings and measurments that worked best for his cars. He said:
"To set the height hold the cover vertically with the gasket in place. Measure from the bottom of the base with gasket, to the bottom of the float with the float just resting on the spring loaded ball."
Bryan recommended settings of 41mm (tab barely touching ball valve) and 51mm with the float pulled down by gravity. (See post #10)
In an another post (#28) by Michael Caputo, Michael gives a link ([url=http://www.mgexperience.net/phorum/read.php?1,1776228,1776310#msg-1776310][/url]) that states:
"Float level is measured from the float's bottom edge to the bottom surface of the float bowl cover without the gasket installed."
Does anyone know which is correct (gasket on/off) or does it matter that much?
Wayne
Jimmy:
Thanks for your input. My carb has a brass float. I was previously advised to use 41mm and 51mm for the F50 (primary) and F6 (secondary) emulsion tube configuration. Your post assumes "plastic" floats. Am I correct using the 41/51mm measurments?
Wayne
No matter if it is a Water/Manual or electric choke, or plastic or brass floats PER WEBER...
Check out this link.. This should explain everything..
http://www.mgexperience.net/article/all/WeberCalibrations.pdf
Jimmy:
I see what you are saying from the Weber table. I have a manual choke on my carb. If I am correctly reading the table, the 46.5/36.5 is the factory setting. That setting is also paired with a 165 primary air correction jet when using F50/F6 emulsion tubes and likewise 055 primary idle jet. All of the factory parts are in my carb without buying new ones. Some of the guys recommended the following configuration as the one that works best on the MGB 1800cc engine:
Idle jets: 060 (pri), 050 (sec)
Main jets: 140 (pri), 135 (sec)
Air Correction jets: 170 (pri), 160 (sec)
emmulsion tubes: F50 (pri), F6 (sec)
float setting: 51/41
This particular configuration does not match any "factory" configuration for a manual choke and brass float. Is it possible that the other guys are customizing the factory configuration to make the carb more efficient on the MGB 1800cc engines. Weber may have designed the carb to work on other cars besides the MGB to increase their market. I don't know. I'm a tinkerer with very little experience with the MG.
Wayne
Wayne,
I have the exact match up that you have and I set my float height to what weber stated and "Christine" runs great. Float height has to do with the emmulsion tubes and if you haven't messed with them, there should be no need to change the float height from spec. Imagine if you will two cups side by side with a tube connecting them at the bottom. As you fill one cup, the other one fills up to match. This is why if you change emmulsion tubes the float height needs to be adjusted due to the holes in the emmulsion tubes going up or down.
Bottom line is this.. If you float height is too high the sound you hear will be like sucking thru a straw. The air coming down the air corrector and the fuel sitting in your emmulsion tube create a fine mist if your float is set correctly. If not, it sounds like sucking thru a straw. Hope this helps..
Jimmy:
I actually have a slightly different setting than what I posted above. This is what I found in my carb when I checked everything out. According to Weber's table, it looks like I have a factory set up:
My carb:
Idle jets: 055 (pri), 050 (sec)
Main jets: 140 (pri), 135 (sec)
Air Correction jets: 165 (pri), 160 (sec)
emmulsion tubes: F50 (pri), F6 (sec)
float setting: 51/41 (recently adjusted by me, not sure what it was prior to setting)
Is this what you have (with the exception of the 51/41 float setting)?
Yes that was my initial set up.. I have since moved up one size on my idle jet (MAIN).
In Jimmy's diagram above (post #42)take a look at the needle valve assymbly (labled V, S and Sf). When you adjust the float to the 36.5 (up position)should the telescoping needle valve(S) be extended all the way downward (carb mounted)and the float tab touching (but not compressing)the spring-loaded valve ball(Sf)? Obviously, this is important since the needle valve can telescope through a large range (about 5 mm) in the housing (V). The ball itself can also compress about a millimeter. Depending on the positioning of everything you could be in error roughly 6 mm. Very important information.
I actually tried a 057 first, but the 060 put my AF mixture and idle speed dead center where it should be. I hope this helps.
Wayne, the DGV is offered for a multitude of vehilcles which is why I wanted you to check the jetting. To see if it was even in the ballpark of being set up for a MGB. If you search this site you will see where people have reported jets sizes all over the board and all say it runs great. 95% of the problems you were having more than likely had to do with the crud. It sounds like Jimmy's data is more up to speed on the 5A so he has you in good hands.
Bryan:
I totally agree. The problem is crud build up. I just hope it's not hiding somewhere that I can't see. I'm going to put the new jets in tomorrow. I'm still a bit worried about the float issue. I might call Pierce and see how to measure the tab position relative to the needle valve position.
Wayne
I spoke to a technical representative at Pierce today. Here's what I found out:
1. The brass floated DGV carb should be set at 41 mm / 51 mm. (tab NOT compressing the ball valve on the needle valve). The needle valve will be telescoped inward on the needle valve mounting.
2. Measurements should be made from the base surface with the gasket on, not off.
3. The above measurements of 36.5 / 46.5 mm is only for a "composite" type floated carb using F50 and F6 emulsion tube pairing. This does not apply to the brass floated carbs.
I hope this helps. I didn't realize there were so many different configurations of the DGV carb.
I now have this one set up as suggested with the 060 main idle jet instead of the 055. I also replace my165 primary air correction jet with a 170. Provided all of the crud is now removed, hopefully she'll run smoothly. I'll let you know what happens.
Wayne
Bryan, James, David and Ray:
Thanks for all of your expert advice!! I finaly have the carb working smoothly. I took the car for about a 5 mile run. Outside of the throttle lever sticking a bit, it ran very well. I'm going to spray a little lubricant on the lever and put a stiffer spring on it. I think that will put the final touch on it.
This was quite a challenge. There's no way I could have figured solved this problem without your help.
Wayne
